Re: Cygwin licensing and redistribution, GPLv2, GPLv3

[tom honermann <tom dot honermann at Oracle dot COM>]

On 1/27/2011 4:14 PM, Eric Blake wrote:
> On 01/27/2011 04:57 PM, tom honermann wrote:
> > I've been looking into Cygwin licensing and redistribution regarding the
> > Cygwin DLL and various GNU utilities.  The current Cygwin license
> > (http://cygwin.com/licensing.html) states (and I'm paraphrasing) that
> > programs that use the Cygwin DLL do not need to be licensed under GPLv2
> > (or compatible) so long as they are distributed with a license that
> > meets the OSI's open source definition AND that the cygwin DLL is not
> > distributed with the program.  With the release of the GPLv3 license and
> > subsequent re-licensing, some of the GNU utilities included with the
> > Cygwin distribution are now GPLv3 (or later).  The GPLv2 and GPLv3
> > licenses are not compatible
> > (http://www.gnu.org/licenses/gpl-faq.html#v2v3Compatibility).
> Wrong list.  Ask on cygwin-licensing.
Thanks Eric.  Copying cygwin-licensing instead now...
> > The way I interpret this, this effectively means that no entity other than RedHat
> > can distribute GPLv3 GNU utilities dynamically linked with the Cygwin
> > DLL and include the Cygwin DLL with the GNU utilities (without
> > additional permissions by RedHat).  This also means that no entity other
> > than RedHat can redistribute the RedHat Cygwin distribution or build
> > their own Cygwin distribution unless all programs are linked with a
> > static version of the Cygwin library (again, without additional
> > permissions by RedHat).  Does this sound right?  If so, is this an
> > intentional property of the Cygwin license?
> Short answer - wrong interpretation.  The cygwin license exception
> specifically states that a GPLv3 program (by virtue of being an OSI
> approved license) can be linked against cygwin and distributed as though
> the GPLv2 of cygwin were not present.  Therefore, the GPLv2-only nature
> of cygwin does not interfere with the GPLv3 license of the program.
The exception posted at http://cygwin.com/licensing.html explicitly 
states "Note that this
does not apply to the Cygwinâ DLL itself.  If you distribute the Cygwinâ 
DLL, either in
its original form or in a form modified by you, you must adhere to the 
terms of the GPL".

I've been reading this as requiring that distribution of programs that 
use the Cygwin DLL
either must not distribute the Cygwin DLL (ie, the program must be 
installed and used
with an existing Cygwin installation), or, if the distribution does 
include the Cygwin DLL,
then uses of the Cygwin DLL must be in accordance with the GPL(v2).  
Perhaps this
statement is only meant to indicate that changes to the Cygwin DLL 
itself must be
licensed in accordance with the GPL(v2)?  As stated, it isn't clear that 
the open source
licensing exception applies to copies of the Cygwin DLL distributed by 
entities other
than Red Hat.